Reinforced concrete piles



Oct. 30, 1962 A. B. HOLMES' 3,060,694

REINFORCED CONCRETE FILES Filed Oct. 29, 1958- Inventor feed tube is filled with concrete and Withdrawn.

United States Patent Ofifice 3,060,694 Patented Oct. 30, 1962 3,060,694 REINFORCED CONCRETE FILES Arthur Brannam Holmes, Swanland, North Ferriby, England, assignor to Holmpress Piles Limited, Hull, England, a British company Filed Oct. 29, 1958, Ser. No. 770,406 Claims priority, application Great Britain Oct. 31, 1957 6 Claims. (Ci. 61-5362) This invention concerns reinforced concrete piles of the type which are formed in situ.

It is common practice to form such piles in the following manner. A bore is formed in the ground by driving or boring using a tube which serves as a lining for the bore. A metal reinforcement is positioned in the bore and the bore is filled with concrete. The lining tube is then withdrawn and the concrete is expanded so as to key into the earth walls of the bore by driving using a drive feed tube of external diameter slightly less than the internal diameter of the metal reinforcement, which acts as a guide for the drive feed tube. The drive If desired, the process of expanding the concrete is repeated, especially if the bore has been made in soft ground.

In order to ensure that the reinforcement is maintained substantially vertical and covered by concrete after the lining tube has been withdrawn, spacing elements are provided in the form of triangular or prismatic precast concrete spacers having tie wires embedded therein by which the elements are secured to the metal reinforcement. The spacers are secured to the outside of the metal reinforcement so as to extend from it into close proximity with the walls of the lining tube. When the lining tube is withdrawn, the spacers are left in situ.

The use of such spacing elements suffers from a number of disadvantages. They are relatively insecure and can easily be displaced by the incoming concrete. There is no real assurance of any permanent adhesion between the pre-cast concrete spacing elements and the concrete which is poured into the bore. Moreover, there is a tendency for the added concrete to arch over the precast concrete spacing elements and a void may be created beneath each pre-cast concrete spacing element, thus weak ening the finished pile. The danger of void formation may be reduced by increasing the mobility of the concrete mix i.e. increasing its water content, but any increase in water content may militate against the strength of the concrete. Even if the voids are avoided, the presence of the spacing elements in the finished pile gives rise to a lack of uniformity in the pile. Finally, considerable time is consumed in attaching the spacing elements to the reinforcement and in ensuring that a proper number of such spacing elements are employed.

An object of the present invention is to provide a method of forming a reinforced concrete pile Whereinthe use of spacers attached to the reinforcement is obviated.

A further object of the present invention is to provide a method of forming a reinforced pile wherein a reinforcement of greater simplicity can be employed with consequential saving in cost.

Yet a further object of the present invention is to provide a method of forming a reinforced concrete pile wherein a lining tube of a novel construction is employed.

According to the present invention a driving or lining tube is provided with spacing elements in the form of longitudinal ribs permanently or detachably secured to its inner surface.

The invention includes a method of forming a reinforced concrete pile using such a tube.

Said spacing elements may take the form of a series of knife-like radially disposed longitudinal ribs extending along the inside of the lining tube in a generally axial .tube at intervals of envisaged.-

direction. In order to facilitate removal of the lining tube without creating voids in the concrete it will generally be found highly desirable to provide ribs which are substantially parallel to one another.

Said spacing elements may be substantially co-extensive with the length of any lining tube or sectioned portion thereof. Alternatively, the spacing elements may be interrupted so as to provide two or more circumferential groups suflicient in aggregate to keep the reinforcement in proper alignment within the bore. In this latter event it is necessary that-the axial length of any group of spacing elements shall be slightly greater than the pitch of the hoops or spiral used in the reinforcement. The ribs need not necessarily be opposite to each other but may be staggered.

The number of spacing elements or longitudinal ribs disposed on the inner circumferential surface of the lining tube is only critical insofar as to ensure that the reinforcement is kept in correct alignment with the lining tube. Thus it will be appreciated, subject to due regard being paid to the respective diameters of the lining tube andreinforcement, that as small a number as three spacing elements may be employed if separated from each other around the circumference of the lining Generally speaking, the relationship between the number of spacing elements employed and the respective diameters of the lining tube and reinforcement should be such that the virtual circle distance extending between any two adjoining spacing elements should be slightly less than the overall diameter of the reinforcement.

Where the spacing elements are arranged in two or more circumferential groups, it is preferred that each element shall have a length not exceeding one tenth of the length of the tube, a maximum depth of between onetenth and one-twentieth of the length of the element and a thickness not exceeding one quarter of the depth of the element.

The spacing elements need not be of uniform dimensions. For example, they can consist of ribs having tapered or chamfered end portions.

Whilst it will generally be found more convenient to provide the lining tube with spacing elements formed integral therewith, the use of detachable spacing elements is envisaged, especially where the lining tube is composed of two or more inter-engaging sections which are detached from one another during withdrawal. In such an event, the use of spacing elements bridging the union between two inter-engaging sections of lining tube, but capable of being detached from the composite lining tube before the sections of the latter are disengaged, is

The invention will now be further described by way of example with reference to the accompanying drawings in which:

FIG. 1 is an elevation, mainly in section, of a driving or lining tube,

FIG. 2 is an elevation on an enlarged scale of part 0 the tube shown in FIG. 1,

SIG. 3 is a section taken on the line IIIIII of FIG. 2, an

FIG. 4 is a sectional elevation of a bore containing a driving or lining tube according to the invention.

Referring firstly to FIGS. 1 to 3, a driving or lining tube 5 has a length of 27 ft., an outside diameter of 16" and an inside diameter of 15". The tube has an enlarged diameter upper end portion 5a to receive a drivmg means (not shown). Spacing elements 6, which have a length of 2 ft., 21 maximum depth of 1 /2", and a thickness of A", are mounted on the inner surface of the tube 5 and are provided with tapered or chamfered end portions 6a. The lower spacing elements are a clear 5 ft. above the lower end of the tube and a clear ft. below the upper spacing elements. The spacing elements may conveniently be attached to the tube by welding and it is important that they should be in substantial alignment with the longitudinal axis of the tube.

It is to be clearly understood that the drawings are not to scale. The dimensions have been included to show the relative proportions and location of the spacing elements on a typical driving tube. They have been given as a guide only and must not be interpreted in any limiting sense. If a 45 ft. driving or lining tube were used, three or more sets of spacing elements could conveniently be used in place of the two sets shown in the drawings.

In FIG. 4, a tube 5 is shown positioned in a bore 7, in which a reinforced concrete pile is to be formed. A metal reinforcement 8 is maintained in a substantially vertical position within the bore by means of the spacing elements 6 of the tube 5 While concrete is poured into the bore 7. Since the spacing elements are knifelike, the amount of disturbance suffered by the concrete when the tube 5 is subsequently withdrawn from the bore is reduced to a minimum. The length of each spacing element 6 exceeds the distance between adjacent hoops 8a of the metal reinforcement 8.

The spacing elements of the present invention form an integral part of the driving or lining tube and are in consequence withdrawn with the tube. Hence, the possibility of any void being established beneath the spacing elements is substantially eliminated and the 1 /2 concrete cover of the reinforcement normally demanded in concrete work can be achieved with much greater certainty than when using the aforementioned tie-on precast concrete spacing elements. In particular, this cover may be achieved before the concrete exudes from the lining tube. In addition to facilitating correct alignment of the metal reinforcement in the bore and permitting good concrete cover of the metal reinforcement, the use of the knife-like spacing elements of the present invention enables a high degree of uniformity to be achieved in the finished pile since these elements do not remain in the finished pile.

I claim:

I. An assembly of pile forming elements comprising a retractable lining tube temporarily located in a bore in the ground, said tube having at least two vertically spaced separate groups of spacing elements in the form of longitudinal ribs secured to its inner surface, each of said groups comprising at least three spacing elements and a reinforcement of longitudinal rods and vertically spaced circumferential hoops for said pile centrally located within said tube, said spacing elements engaging the hoops to centrally locate the reinforcement in the tube.

2. The improved retractable cylindrical lining tube defined in claim 1 wherein each of said longitudinal ribs has a length less than one-tenth of the length of the tube, a maximum depth of between one-tenth and onetwentieth of the length of the rib and a thickness of less than one-quarter of the depth of the rib.

3. The improved lining tube defined in claim 1 wherein each of said longitudinal ribs has its end portions tapering inwardly from the inner wall of said tube.

4. The improved lining tube defined in claim 1 wherein each of said longitudinal ribs has a length less than one-tenth of the length of the tube and the distance be tween the end of the tube and the nearest circumferential group of ribs is less than the distance between the two circumferential groups of ribs.

5. An assembly of pile forming elements comprising a retractable lining tube located in a bore in the ground, said tube having spacing elements in the form of longitudinal ribs secured to its inner surface in at least two circumferential groups, each group comprising at least three spacing elements and a reinforcement for said pile centrally located within said tube by means of said spacing elements, said reinforcement comprising a uniform skeletal structure of generally longitudinal rod and circumferential hoop configuration, the axial length of any circumferential group of spacing elements being greater than the distance between adjoining hoops in said skeletal structure, and the virtual circle distance between any two adjacent spacing elements being less than the overall diameter of the reinforcement.

6. In apparatus for use in the construction of a reinforced concrete pile comprising at least two interengageable sections of a retractable cylindrical lining tube to be driven into a bore in the ground and a skeletal reinforcement of longitudinal rods and circumferential hoops vertically disposed within and equally spaced from the inner surface of said tube, wherein said tube is thereafter filled with concrete and withdrawn from said bore leaving said skeletal reinforcement embedded in concrete within said bore to form the finished pile, the improvement whereby any radial movement of said skeletal metal reinforcement relative to the inner surface of said tube is obviated during the filling of said tube and the withdrawal of said tube sections from said bore and said reinforcement is evenly embedded in said concrete, comprising a first group of spacing elements in the form of longitudinal ribs secured to and circumferentially spaced about the inner wall of each of said interengageable sections adjacent the free end thereof to engage the hoops and centrally locate the reinforcement in the tube; and a second group of spacing elements in the form of longitudinal ribs bridging the junction between the inner surface of each pair of interengageable sections and secured thereto, said second group of spacing elements being detachable from at least one of said inner tube surfaces before said sections are disengaged.

References Cited in the file of this patent UNITED STATES PATENTS 843,218 Lally Feb. 5, 1907 858,742 Moran July 2, 1907 1,080,283 Kenny Dec. 2, 1913 1,830,651 Prankignoul Nov. 3, 1931 2,146,645 Newman Feb. 7, 1939 FOREIGN PATENTS 655,614 Germany Jan. 19, 1938 

